WO 03/088011 A2 describes a mobile electronic computing unit that can be held in one hand, in particular in the manner of a personal data assistant (PDA) or hand-held computer, with a software-controlled processor unit, at least one memory device connected to it for the storage of software modules and/or data to be processed, at least one display device for the visually detectable output of information and with at least one input device to at least affect the operational functions of the computing unit and/or to input data, whereby the display device and the input device are combined in terms of their components or functions in the form of a touch-sensitive screen, for example a touchscreen, and with at least one standardly configured interface on the housing of the arithmetic unit, provided for connecting peripheral, electronic or electrical devices, such as e.g. a personal computer, whereby the standardly configured interface or an independently configured interface is provided for connecting at least one safety switching element in the form of an emergency off switch and/or an enabling switch.